Hitherto, aromatic polyimides have widely been used as protecting materials, insulating materials and adhesives in the filed of electronic appliances and also as films or construction materials in other various fields, because of their high mechanical strength, heat-resistance and solvent-resistance. However, conventional polyimides have various drawbacks that the shaping workability is poor, the flexibility is poor, the wet stability is poor and the adhesiveness to inorganic materials such as silicone wafer or glass is insufficient. In order to overcome the drawbacks, modified polyimides having various chemical structures have been produced and studied in these days. Above all, a technique of producing a polyimide/polysiloxane block copolymer from a polyimide precursor to be obtained by substituting a part of the diamine component of a starting material of a polyimide by a polysiloxane having a diamino group at the both terminals thereof has been proposed, for the purpose of improving the flexibility and adhesiveness to inorganic materials among the necessary properties of polyimides. (For instance, refer to JP-A-57-143328, 58-7473, 58-13631, 61-83228 and 61-118424. The term "JP-A" as used herein means an "unexamined published Japanese patent application".) However, such block copolymers may have improved flexibility and adhesiveness but, on the other hand, have a problem that the filming capacity is lowered with increase of the siloxane content in the copolymer.
There is another proposal of using an aromatic polyimide as a gas-separating film material. (Refer to JP-A-57-15819.) As the film of the kind made of such an aromatic polyimide has an excellent selective permeability especially to hydrogen gas, it has already been put to practical use. Since the gas permeability coefficient of such an aromatic polymide film is generally small, the film may well be applied to a gas having a relatively small molecular size and having a high diffusibility through the film, such as hydrogen gas. However, the film is unsuitable to separation of any other gas, such as oxygen or carbon dioxide because of such a small gas permeability coefficient. Additionally, there are few examples of using a polyimide film as a liquid-separating film. As one example, there is a report relating to separation of a water/ethanol mixture with a polyamic acid film which has been controlled with respect to its imidation percentage (refer to Polymer Preprints, Japan, Vol. 36, 1987, page 2021). However, also in the case, as the permeability coefficient of the reported film is relatively small, the film could not be said to be practically usable.
In order to elevate the gas and liquid permeability of a polyimide film, copolymerization with a material having a high substance permeability like the above-mentioned polyimide/polysiloxane copolymer could be proposed. In fact, however, there is no report relating to gas or liquid separation with such a copolymer up to this date because of the problem on the filming property of the copolymer. On the other hand, the present inventors previously investigated various matters for the purpose of obtaining new film materials of aromatic polyimides which have excellent mechanical strength, heat-resistance and solvent-resistance of aromatic polyimides of themselves and have sufficient liquid permeability and separatability of a practical level. As a result, they have found that production of a polysiloxane macromonomer having a diaminophenyl group at one terminal thereof and having an organosiloxane repeating unit is possible, that polycondensation of the macromonomer gives a siloxane-containing polyimide via a siloxane-containing polyimide precursor, and that the film to be obtained from the resulting siloxane-containing polyimide has excellent mechanical strength, heat-resistance, solvent-resistance and flexibility and also has an excellent gas or liquid selective permeability (refer to JP-A-1-204931).
On the other hand, in the field of a liquid crystal-aligning agent, an organic resin film such as a polyimide resin film or the like has heretofore been used most popularly as a substrate-treating agent, which is applied to a transparent substrate such as a transparent glass or plastic film as combined with a transparent electrode so as to orient nematic liquid crystal molecules almost in parallel to the treated substrate.
In the case, it is known that the organic resin film as formed on the substrate is rubbed with a cloth in a determined direction, whereby the liquid crystal molecules as provided on the substrate are oriented to the rubbed direction to simultaneously yield a liquid crystal tilt angle of generally from 1 to 3 degrees to the surface of the substrate.
As a method of greatly tilting and orienting liquid crystal molecules to the substrate, a method of depositing an inorganic film such as a silicon oxide film on a substrate by vapor deposition has heretofore been known.
The present inventors earnestly investigated various polyimides so as to further improve the poor wet stability of polyimides of themselves as well as the surface characteristic and separation characteristic of siloxane-containing polyimide films by introducing a fluorine-containing group into the side chain of general polyimides or the above-mentioned siloxane-containing polyimides to thereby elevate the water-repelling property of the surface of the film to be obtained from the resulting polyimide. As a result, they have found a technique of producing a novel fluorine-containing diaminobenzene derivative having a perfluoroalkyl group, and a technique of producing a novel fluorine-containing polyimide and a novel polyimide having both a fluorine-containing group and a siloxane chain in the side chain thereof by polycondensation of the said novel derivative followed by imidation of the resulting polycondensate, and they have further found that the polyimides thus obtained have a high water-repelling property because of the characteristic of the fluorine-containing group therein.
In the filed of a liquid crystal-aligning agent, a method of rubbing an organic resin film as formed on a substrate has heretofore been carried out. In the method, however, it is difficult to sufficiently largely tilt and orient the liquid crystal molecules as provided on the rubbed film.
On the other hand, a method of depositing an inorganic film on a substrate by vapor deposition is more complicated than the rubbing method and therefore it is not always a suitable method in practical industrial production of liquid crystal devices.
Under the situation, it has been found that a satisfactory liquid crystal-aligning agent for liquid crystal cells can be produced from the polyimides of the present invention. Precisely, the liquid crystal-aligning agent containing the novel polyimide of the present invention yields a sufficiently large tilt angle when applied to a substrate of liquid crystal cell. On the basis of the findings, the present inventors have achieved the present invention.
JP-A-62-142099 has proposed a liquid crystal-aligning agent, which comprises a reaction product of a long-chain alkylamine and a polyimide resin precursor. JP-A-64-25126 has proposed a liquid crystal-aligning agent, which comprises a polyimide as derived from a starting material of an alkyl group-having diamine.
However, it is unknown that a liquid crystal-aligning agent, which comprises a polyimide having a fluorine-containing group and/or a siloxane chain in the side chain thereof, the polyimide being obtained from a starting material of a fluorine-containing diaminobenzene derivative and/or a siloxane-containing diaminobenzene derivative, like the present invention, yields an extremely large tilt angle of liquid crystal molecules.